使用苹果公司的新Combine框架时如何防止强参考周期(.assign引起问题) [英] How to prevent strong reference cycles when using Apple's new Combine framework (.assign is causing problems)
问题描述
我不太了解如何正确地将订阅者存储在类中,以使它们持久化,但又不阻止对象被初始化.这是一个对象不会取消初始化的示例:
I don't quite understand how to properly store subscribers inside a class so that they persist but don't prevent the object from being deinitialized. Here's an example where the object won't deinit:
import UIKit
import Combine
class Test {
public var name: String = ""
private var disposeBag: Set<AnyCancellable> = Set()
deinit {
print("deinit")
}
init(publisher: CurrentValueSubject<String, Never>) {
publisher.assign(to: \.name, on: self).store(in: &disposeBag)
}
}
let publisher = CurrentValueSubject<String, Never>("Test")
var test: Test? = Test(publisher: publisher)
test = nil
当我将 assign
替换为 sink
(在其中我正确声明了 [weak self]
)时,它实际上确实可以正确初始化(可能是因为 assign
会以导致问题的方式访问 self
.
When I replace the assign
with a sink
(in which I properly declare [weak self]
) it actually does deinit properly (probably because the assign
accesses self
in a way that causes problems).
例如,在使用 .assign
时如何防止强参考循环?
How can I prevent strong reference cycles when using .assign
for instance?
谢谢
推荐答案
您可以用接收器(.sink)替换.asign(to :),其中其关闭中的[weak self]会阻止内存循环.在Playground尝试一下,看看有什么不同
you can replace .asign(to:) with sink where [weak self] in its closure brake the memory cycle. Try it in Playground to see the difference
final class Bar: ObservableObject {
@Published var input: String = ""
@Published var output: String = ""
private var subscription: AnyCancellable?
init() {
subscription = $input
.filter { $0.count > 0 }
.map { "\($0) World!" }
//.assignNoRetain(to: \.output, on: self)
.sink { [weak self] (value) in
self?.output = value
}
}
deinit {
subscription?.cancel()
print("\(self): \(#function)")
}
}
// test it!!
var bar: Bar? = Bar()
let foo = bar?.$output.sink { print($0) }
bar?.input = "Hello"
bar?.input = "Goodby,"
bar = nil
它打印
Hello World!
Goodby, World!
__lldb_expr_4.Bar: deinit
所以我们没有内存泄漏!
so we don't have the memory leak !
最终在forums.swift.org上,有人做出了一个可爱的
finally at forums.swift.org someone make a nice little
extension Publisher where Self.Failure == Never {
public func assignNoRetain<Root>(to keyPath: ReferenceWritableKeyPath<Root, Self.Output>, on object: Root) -> AnyCancellable where Root: AnyObject {
sink { [weak object] (value) in
object?[keyPath: keyPath] = value
}
}
}
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